Phased array antennas are useful for providing high quality, electronically scanned beams. However, such antennas require the distribution of RF energy to a large number of elements in the array.
One solution to this problem is the space fed antenna wherein a second, usually smaller, array, the excitation array, radiates energy across a space after which it is coupled to and re-radiated by the primary, or radiation array. Thus, power distribution to the radiation array requires no direct physical connections.
Typically, each element of the radiation array in a space fed antenna is phase controlled, as in a phased array, and the radiation elements may also be amplitude controlled. In addition, it is sometimes necessary to apply phase and/or amplitude control to the excitation array elements. Thus, the number of high resolution phase shifters and amplitude settings required for an E-scan, space fed antenna can be quite large.